U.S. patent application number 15/411734 was filed with the patent office on 2017-10-26 for high capacity easy release extended use adhesive devices.
This patent application is currently assigned to University of Massachusetts. The applicant listed for this patent is University of Massachusetts. Invention is credited to Michael D. Bartlett, Andrew B. Croll, Alfred J. Crosby, Daniel King.
Application Number | 20170306189 15/411734 |
Document ID | / |
Family ID | 46207638 |
Filed Date | 2017-10-26 |
United States Patent
Application |
20170306189 |
Kind Code |
A1 |
Crosby; Alfred J. ; et
al. |
October 26, 2017 |
HIGH CAPACITY EASY RELEASE EXTENDED USE ADHESIVE DEVICES
Abstract
The invention provides novel devices, systems, designs,
materials and fabrication methods that enable high-load capacity,
easy release, and suitable for extended/repeated use in a variety
of applications.
Inventors: |
Crosby; Alfred J.; (Amherst,
MA) ; Bartlett; Michael D.; (Amherst, MA) ;
Croll; Andrew B.; (West Fargo, ND) ; King;
Daniel; (Sunderland, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Massachusetts |
Boston |
MA |
US |
|
|
Assignee: |
University of Massachusetts
Boston
MA
|
Family ID: |
46207638 |
Appl. No.: |
15/411734 |
Filed: |
January 20, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13878405 |
Jun 24, 2013 |
9574113 |
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PCT/US2011/057309 |
Oct 21, 2011 |
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15411734 |
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61405544 |
Oct 21, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 5/02 20130101; B32B
37/12 20130101; C09J 2427/001 20130101; C09J 7/38 20180101; C09J
2427/006 20130101; C09J 2301/204 20200801; C09D 5/20 20130101; B32B
2307/748 20130101; A44B 18/0069 20130101; Y10T 428/2481 20150115;
Y10T 24/33 20150115; Y10T 428/24612 20150115; C09J 7/00 20130101;
C09J 7/21 20180101; C09J 2483/00 20130101; C09J 2483/006 20130101;
B32B 7/00 20130101; C09J 2400/263 20130101; B32B 37/16 20130101;
C09J 7/30 20180101; Y10T 428/2848 20150115; C09J 2433/00 20130101;
C09J 175/04 20130101; C09J 2475/00 20130101; C09J 2301/312
20200801 |
International
Class: |
C09J 7/04 20060101
C09J007/04; C09J 7/04 20060101 C09J007/04; C09D 5/20 20060101
C09D005/20 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] The United States Government has certain rights to the
invention pursuant to Grant No. N66001-08-C-2054 from the
Department of Navy to the University of Massachusetts.
Claims
1-130. (canceled)
131. A releasable surface-adhesive device, comprising: an adhesive
pad, comprising: a planar backing layer; a planar layer of an
elastic material having an adhesive surface on at least one side
for adhering to a target surface, wherein a side of the planar
layer of the elastic material opposing the adhesive surface is
applied onto the backing layer, and wherein the backing layer has a
higher in-plane stiffness than the planar layer of the elastic
material.
132. The releasable surface-adhesive device of claim 131, wherein
the planar layer of the elastic material comprises two or more
separate smaller elastic material layer units.
133. The releasable surface-adhesive device of claim 131, further
comprising a flexible tether attached to and extending from the
backing layer of the adhesive pad
134. The releasable surface-adhesive device of claim 133, wherein
an angle between the tether and the adhesive pad is adjustable.
135. The releasable surface-adhesive device of claim 133, further
comprises a holding component attached to the tether for connecting
an object to the device.
136. The releasable surface-adhesive device of claim 133, wherein
the tether comprises at least one of fabric, rope, fiber, plastic
sheet, tubing, rods, metal foil, chains, non-woven textile, cable,
and leather.
137. The releasable surface-adhesive device of claim 133 wherein
the tether is attached to the adhesive pad away from an edge of the
adhesive pad.
138. The releasable surface-adhesive device of claim 133, wherein
the tether is attached to the adhesive pad at the center of the
adhesive pad.
139. The releasable surface-adhesive device of claim 131, wherein
the planar layer of the elastic material has a uniform thickness
between 0.0001 cm to 0.1 cm.
140. The releasable surface-adhesive device of claim 139, wherein
the elastic material has an elastic modulus between 0.05 MPa to 50
MPa.
141. The releasable surface-adhesive device of claim 140, wherein
the elastic material comprises at least one of a siloxane-based
elastomer, an urethane-based elastomer, an acrylate-based
elastomer, a polydimethylsiloxane (PDMS), a block copolymer
elastomer, a polyurethane, styrene-butadiene-styrene, and a natural
rubber.
142. The releasable surface-adhesive device or method of any of
claim 141, wherein the backing layer comprises at least one of a
fabric, foil, sheet, and film.
143. A method comprising: attaching a flexible tether to the
adhesive pad of the releasable surface-adhesive device of claim
131.
144. A method for making a releasable surface-adhesive device,
comprising: applying an elastic material to a planar backing layer;
curing the elastic material to form an adhesive pad having a planar
layer of the elastic material applied onto the planar backing
layer, wherein the backing layer has a higher in-plane stiffness
than the elastic planar layer.
145. The method of claim 144, further comprising attaching a
flexible tether to the adhesive pad.
146. The method of claim 145, wherein the tether comprises at least
one of fabric, rope, fiber, plastic sheet, tubing, rods, metal
foil, chains, non-woven textile, cable, and leather.
147. The method of claim 145, wherein the tether is attached to the
adhesive pad away from an edge of the adhesive pad.
148. The method of claim 145, wherein the tether is attached to the
adhesive pad at the center of the adhesive pad.
149. The method of claim 144, wherein the planar layer of the
elastic material has a uniform thickness between 0.0001 cm to 0.1
cm.
150. The method of claim 149, wherein the elastic material has an
elastic modulus between 0.05 MPa to 50 MPa.
151. The method of claim 150, wherein the elastic material
comprises at least one of a siloxane-based elastomer, an
urethane-based elastomer, an acrylate-based elastomer, a
polydimethylsiloxane (PDMS), a block copolymer elastomer, a
polyurethane, styrene-butadiene-styrene, and a natural rubber.
152. The method of claim 151, wherein the backing layer comprises
at least one of a fabric, foil, sheet, and film.
Description
RELATED APPLICATIONS
[0001] This application is a continuation and claims the benefit
under 35 U.S.C. .sctn.120 of U.S. application Ser. No. 13/878,405
filed on Jun. 24, 2013, which is a National Stage of
PCT/US2011/057309 filed Oct. 21, 2011, which claims the benefit of
priority under 35 U.S.C. .sctn.119(e) to U.S. Provisional
Application Ser. No. 61/405,544 filed Oct. 21, 2010, each of which
is herein incorporated by reference in its entirety.
TECHNICAL FIELD OF THE INVENTION
[0003] The invention generally relates to designs, devices,
materials and methods useful for weight-bearing. More particularly,
the invention relates to designs, devices, systems, materials and
fabrication methods that provide adhesive devices that are
high-load bearing, easy release, and suitable for extended/repeated
use in a variety of applications.
BACKGROUND OF THE INVENTION
[0004] Adhesive materials that can support high capacity loads have
traditionally been sought. Pressure sensitive adhesives (PSAs) are
self-adhesives that form a bond when pressure is applied to marry
the adhesive with the adherend. Typically, no solvent, water, or
heat is necessary to activate or stimulate the adhesive to perform.
Conventional PSAs have found use in pressure sensitive tapes,
labels, note pads, automobile interior trims, and a wide variety of
other products. There has been continued effort among the
scientific community to create and produce synthetic materials and
devices that mimic the performance of animals, such as geckos, in
Nature.
[0005] PSAs typically rely on ubiquitous surface force
interactions, such as van der Waals forces, to transfer stress
across an interface. Pressure sensitive adhesives can adhere to a
surface because the adhesive is soft enough to flow, or wet, the
adherend. The adhesive needs to be hard enough to resist flow when
stress is applied to the bond at the interface. PSAs exhibit
viscoelastic (viscous and elastic) properties, both of which may be
used for creating proper bonding.
[0006] Currently, PSAs are mainly fabricated from soft,
viscoelastic polymer materials (e.g., coatings), which are used
either independently or in conjunction with a backing material,
such as a stiff film or cloth. To control the level of adhesion,
PSAs alter their bulk properties by relying upon a complex
formulation of both elastic and viscoelastic components to
delicately balance the ability of a material to form an interface
(or "wet a surface") and the resistance to separation once the
interface is formed. (Benedek, et al. Eds. 2009 Handbook of
Pressure Sensitive Adhesives and Products Series, CRC Press: Boca
Raton; Pocius, 2002, Adhesion and Adhesives Technology: An
Introduction, Hanser Publ.: Munich; Crosby, et al. 1999 J. Poly.
Sci. Part B: Polym. Phys. 37, 24, 3455-3472; Creton, 2003
"Materials Science of Adhesives: How to Bond Things Together." MRS
Bulletin 28, 6, 419-421; Creton, 2003 "Pressure-sensitive
adhesives: An introductory course." MRS Bulletin 28, 6, 434-439;
Creton, et al. 2007 "Sticky Feet: From Animals to Materials", MRS
Bulletin 32, 6, all pages; Chan, et al. 2007 "Designing Model
Systems for Enhanced Adhesion." MRS Bulletin 32, 6, 496-503;
Boesel, et al. 2010 Advanced Materials 22, 19, 2125-2137.)
[0007] Among the various aspects of PSA designs, three factors are
typically relevant and emphasized: (1) Conventional PSAs are
viscoelastic to allow the polymer coating to conform easily with
rough a surface while dissipating mechanical energy (i.e.,
pressure) that is required for conformality; (2) A measure for
strong PSA materials is tack energy, which is the total energy
dissipated during the separation of a PSA/substrate interface; (3)
High tack PSAs are typically not conducive to multiple loading
applications due to the irreversible (i.e. inelastic) materials
processes that are used to produce high levels of tack.
[0008] To develop adhesive material systems that overcome some of
the disadvantages of conventional PSAs, much research has focused
on the development of gecko-like adhesive systems. Some key
attributes of both conventional PSAs and ideal gecko-like adhesives
are provided in the following table:
TABLE-US-00001 Ideal Property Conventional PSA "Gecko-Like"
Adhesive Max Shear Stress High High Max Normal Stress High High
Peel Resistance High Low (after reaching critical peel angle)
Energy of Separation High Low Reversibility Limited to None High
Time/Temp Dependence High Unknown Impact of Fouling High
Limited
[0009] Additionally, the adhesive surface of geckos, and similar
examples in Nature, is commonly described as "dry", i.e., that
adhesion does not rely upon liquid interactions, liquid-to-solid
transitions like an epoxy, nor does the adhesive surface feel
"tacky" to the touch like a conventional viscoelastic adhesive.
Although such attributes are known and displayed in Nature, the
primary design factors or mechanisms that permit good control of
properties is not known and remains the subject of current research
projects worldwide. To our knowledge, the development of a
synthetic analog to a gecko-like adhesive has not been
demonstrated, in particular one that could be used on macroscopic
length scales.
[0010] There is a significant and ongoing need for designs,
systems, devices, materials and related fabrication methods for
adhesive systems that can be used to easily attach and support high
capacity loads, yet provide simple, non-damaging release and
repeated use while being cost-effective to produce.
SUMMARY OF THE INVENTION
[0011] The invention provides unique releasable adhesive devices
that are useful for attachment to various surfaces and allow
significant weight bearing. The materials, designs, systems, and
related methods of fabrication and production disclosed herein
provide adhesive devices that have high load capacity, are
reusable, easy release and suitable for extended and repeated use.
Attachment pads disclosed herein can be designed, for example, to
fit a number of applications ranging from household weight-bearing
shelves and holders, components for indoor and outdoor climbing
devices, components for transportation, athletic equipment, labels
and advertising posts, automobile interior trims, permanent or
reversible fasteners, as well as instruments and devices for
industrial, commercial, medical or military settings.
[0012] In one aspect, the invention generally relates to a
releasable, surface-adhesive device. The device includes an
adhesive pad and a tether component attached to the adhesive pad.
The adhesive pad includes: a planar backing layer having high
in-plane stiffness; and a planar layer of an elastic material
having an adhesive surface on at least one side for adhering to a
target surface, wherein the elastic material is impregnated onto
the backing layer on at least the side opposing the adhesive
surface. In certain preferred embodiment, the device further
comprises a holding component for load bearing. The holding
component being attachable to the tether component for connecting
an object to the device.
[0013] In another aspect, the invention generally relates to a
releasable, surface-adhesive device. The device includes: a planar
layer comprising an elastic material and having on one side an
adhesive surface for adhering to a target surface and on the other
side a backing layer having high in-plane stiffness, wherein the
elastic material impregnating into the fabric backing layer; and a
holding component attachable to the backing layer for connecting an
object to the device. A portion of the backing layer extends beyond
the layer of the elastic material to form an area of the backing
layer un-impregnated with the elastic material, and the holding
component attaches to the backing layer at such area of the backing
layer un-impregnated with the elastic material.
[0014] In yet another aspect, the invention generally relates to a
releasable, reusable surface-adhesive device. The device includes
an adhesive pad that has a planar layer of an elastic material
having an adhesive surface on one side for adhering to a target
surface; and a planar backing layer having high in-plane stiffness,
wherein the backing layer is impregnated onto the layer of the
elastic material on the side opposing the smooth adhesive surface.
The device further includes a tether attached to the adhesive pad
substantially at the center of the adhesive pad and allowing
adjustment of the angle between the tether and the adhesive pad
from about 0.degree. to about 359.degree..
[0015] In yet another aspect, the invention generally relates to a
releasable, surface-adhesive device. The device includes an
adhesive pad, which has a planar layer of an elastic material
having a microscopically smooth or patterned adhesive surface on
one side for adhering to a target surface; and a planar backing
layer having high in-plane stiffness, wherein the backing layer is
impregnated onto the layer of the elastic material on the side
opposing the smooth adhesive surface. The device further includes a
tether component attached to the adhesive pad; and a holding
component for load bearing. The holding component is attachable to
the tether component for connecting an object to the device.
[0016] In yet another aspect, the invention generally relates to a
method for releasably holding a weight on a surface. The method
includes: (a) providing a releasable, surface-adhesive device
having an adhesive pad comprising a planar layer of an elastic
material having a microscopically smooth adhesive surface on one
side for adhering to a target surface; and a planar fabric backing
layer having high in-plane stiffness, wherein the fabric backing
layer is impregnated onto the layer of the elastic material on the
side opposing the smooth surface; a fabric tether attached to the
adhesive pad; and a holding component for load bearing attachable
to the fabric tether for connecting an object to the device; and
(b) attaching the weight to the holding component.
[0017] In yet another aspect, the invention relates to a method for
making a releasable, surface-adhesive device. The method includes:
(a) providing an elastic material; (b) providing a fabric backing
sheet; (c) curing the elastic material to impregnate the elastic
material into at least a portion of the fabric backing sheet to
form a pad having a layer of the elastic material with a smooth
adhesive surface; (d) attaching a weight-holding component to the
fabric backing sheet. The elastic material has an elasticity from
about 0.05 MPa to about 50 MPa, and the layer of the elastic
material has a thickness from about 0.0001 cm to about 0.1 cm.
[0018] In yet another aspect, the invention generally relates to a
method for making a releasable, surface-adhesive device. The method
includes: (a) providing a fabric backing sheet, on one side of
which is placed a substrate layer; (b) providing, on the other side
of the fabric backing sheet, a spacer-defined molding area; (c)
adding an elastic material into the spacer-defined molding area of
the fabric backing sheet; (d) covering the elastic material with a
top cover having a microscopically smooth or patterned surface; (e)
applying pressure against the top cover causing an intimate
interface between the top pad and the elastic material; (f) curing
the elastic material to impregnate the elastic material into at
least a portion of the fabric backing sheet to form a pad having a
layer of the elastic material with a microscopically smooth or
patterned adhesive surface; and (g) attaching a weight-holding
component to the fabric backing sheet. The elastic material has an
elasticity from about 0.05 MPa to about 50 MPa, and the layer of
the elastic material has a thickness from about 0.0001 cm to about
0.1 cm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows a schematic illustration of an exemplary
embodiment of the invention.
[0020] FIG. 2 shows certain design factors and schematic
illustrations.
[0021] FIG. 3 shows a schematic illustration of an exemplary
fabrication process.
[0022] FIG. 4 shows schematic illustrations of various embodiments
of the invention for the pad-tether connection.
[0023] FIG. 5 shows exemplary force vs. displacement measurements
for characterizing maximum force supported under pure shear loading
for "T-pad" structures.
[0024] FIG. 6 shows exemplary maximum shear force supported for
various "T-pad" configurations, live geckos, and non-fabric backed
polymer coatings as a function of the square root of interfacial
area normalized by in-plane compliance.
[0025] FIG. 7 shows exemplary failure force per unit width as a
function of peel angle for various "T-pad" configurations.
[0026] FIG. 8 shows certain examples of complete "T-Pad" structures
supporting loads on various surfaces.
[0027] FIG. 9 schematically illustrates an exemplary embodiment of
fabrication of adhesive pads according to the invention.
[0028] FIG. 10 shows exemplary images of fabric adhesives. (A) A
nylon fabric PDMS adhesive, (B) A carbon fiber/Kevlar plain weave
fabric PDMS adhesive, and (C) a unidirectional carbon fiber
polyurethane adhesive.
[0029] FIG. 11 shows exemplary plot of modulus against frequency
for an example of polyurethane.
[0030] FIG. 12 shows schematic illustrations of an embodiment of
the molding technique for fabricating an adhesive pad according to
the invention.
[0031] FIG. 13 shows exemplary results of a controlled displacement
test (load plotted against extension).
[0032] FIG. 14 shows exemplary results of the repeatability of a
polyurethane adhesive pad undergoing cyclic loading.
[0033] FIG. 15 shows static load test performed with polyurethane
adhesives holding 136 kg.
[0034] FIG. 16 shows exemplary load data from polyurethane
adhesives with a variety of substrates.
[0035] FIG. 17 shows the static load test performed on (A) a center
loaded PDMS adhesive pad holding a 42'' flat panel television and
(B) a center loaded polyurethane adhesive pad holding a hooded
sweatshirt on drywall.
[0036] FIG. 18 (A) shows schematic illustrations of the loading
angle dependence for the high capacity and easy release adhesive
pads. (B) Shows exemplary results of the angle dependence of the
center loaded pad compared to a single slab adhesive pad, where the
center loaded pad maintains a high failure force throughout various
loading angles, while still allowing for easy release.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The invention is based in part on the discovery of novel
designs, systems, devices, and associated materials and methods of
fabrication, which enable large contact surfaces, high-load
capacity, easy release, extended use, and repeated use. More
particularly, the present invention provides a unique, previously
unknown approach to adhesive systems, which is distinctive from
conventional PSA systems and the more recently explored gecko-like
adhesives.
[0038] The invention differs from prior art in the field of PSAs at
least in that the present invention does not rely on viscoelastic
properties to achieve performance controls, as do PSAs. Designs and
systems of the invention allow separation time and energy to be
minimized, while maintaining the ability to support extremely
high-weight loads. Large areas of interfacial contact can be
designed through the combined properties of the soft elastic layer
and the "draping" characteristics of a fabric layer. Furthermore,
the elastic design provides a mechanism for repeated attachment and
separation cycles without degradation in the load bearing capacity
of the adhesive interface.
[0039] In contrast to prior art in the development of gecko-type
adhesives, the designs, systems and methods disclosed herein do not
require the use of surface fibrillar structures to achieve desired
attributes. Following the principles disclosed herein, one may
mimic the engineering design of the toe and leg structures of
common examples in Nature, such as geckos in vertical climbing.
[0040] Other key differences between the present invention and the
prior art relate to, among others, the specific designation of
rotational freedom at continuous junctions, specifications of
stiffness in loading direction with low flexural rigidity
perpendicular to surface of elastic material, and the ability to
achieve high capacity load support under both normal and shear
loading directions with near-zero required "pre-load" (referring to
the amount of force that is required to establish the
adhesive/substrate interface for supporting a given load).
[0041] In one approach of the invention, the adhesive pad system
disclosed herein employs a "dry" adhesive pad structure, sometimes
referred to as a "T-pad", an embodiment of which is schematically
illustrated in FIG. 1. Properly designed, the T-pad device can
support high loads under shear, normal, and multi-mode (i.e. peel)
loadings while requiring minimal forces and energy for release (or
separation) under specifically-designed release strategies.
[0042] The basic structure of the adhesive device is referred to as
the "pad", which is subsequently connected to a tether (e.g., a
synthetic fabric tether), which may be referred to as the "tendon".
The tether should maintain high stiffness along the primary axis of
loading. The connection between the tendon and the pad has
pre-defined dimensions, orientation, and spatial location,
according to particular needs, that can be modified to control the
release strategy and provide tolerated balance of shear and normal
loading.
[0043] This approach represents a unique combination of adhesion
attributes of polymer materials and integrated mechanical designs
through proper conservation of rotational freedom, low flexural
modulus normal to the adhesive interface, and high stiffness in
load bearing directions. A scaling relationship has been developed
by the inventors to provide a framework for understanding the
adhesive performance of the materials devices over a range of size
scales and geometries (FIG. 2). This scaling relationship suggests
that the adhesive capacity (F.sub.C) of an interface is governed by
three simple parameters, which are dependent on both the geometry
and material properties of the interface. To design reversible
adhesives which can adhere to various substrates, the interfacial
interactions (G.sub.C) should rely upon non-specific van der Waals
forces, rendering G.sub.C an ineffective control parameter.
Therefore, to scale F.sub.C for adhesive materials the material
system must not just rely on area on contact (A) or the system
compliance (C) but must develop attributes that increase the A/C
ratio. This presents a challenge; materials must be soft to
increase true contact but stiff to achieve high loads. Soft
materials are able to create large-scale contact but have a high
compliance when loaded, while stiff materials are unable to create
extensive contact; both cases result in a null effect on the A/C
ratio. The current invention provides a mechanism for maximizing
A/C, and most importantly, tuning this governing parameter for
different applications. As schematically illustrated in FIG. 3, an
efficient and effective fabrication method may be used to fabricate
the T-pad. The method involves integrating a thin layer of an
elastic elastomer into a surface of a fabric.
[0044] The tether (tendon) can be connected to the pad through any
suitable methods, such as conventional sewing, stitching, or
gluing, which allows easy control of dimensional, orientational,
and spatial location of the attachment. The attachment should
provide sufficient load sharing and load bearing capacity, which
can be controlled through the stitching pattern, width, and length.
Appropriate stitching patterns include straight stitching, zigzag
stitching, multi zigzag stitch, satin stitching, honeycomb
stitching, ladder stitch, double overlock stitch, and criss-cross
stitching.
[0045] For example, a particularly advantageous tether-pad
connection is a straight-line stitch that is centered on the one
axis of the pad and extends to a length of approximately 2/3 the
chord length perpendicular the second pad axis. The tether-pad
connection should maintain rotational freedom while maintaining
high stiffness in the direction of loading. The tether-pad
connection should preferably maintain equal load sharing along the
entire length of the connection. At a distance sufficiently far
from the tether-pad connection, the tether is integrated into a
load bearing material that has high flexural rigidity and in-plane
stiffness. This rigid terminal material is sometimes referred to as
the "skeleton" (the "holding component"). The connection between
the tether-skeleton should preferably be continuous to ensure equal
load sharing along the length of the connection.
[0046] The invention includes the designs where one T-pad structure
can act independently or in conjunction with an array of T-pad
structures or units (referred to as a "T-surface"), which may be
mounted with rotationally-free joints to a supporting substrate
that can be rigid in one or more directions, for example. For
certain applications, e.g., a large weight bearing shelf, multiple
attachment points for the tether to the adhesive pad may also be
employed.
[0047] FIG. 4 shows schematic illustrations of various T-pad
configurations for the tether-pad connection. Skeleton connection
is not shown. A single slab connection constitutes a continuous
adhesive pad and support backing, which can then be divided into a
larger number of discrete adhesive pads and support backings in
which multiple tendons are used to create different configurations
(e.g., a gradient length series configuration). The off edge tendon
connection and center loaded pad configurations constitute an
adhesive pad and support backing where a planar tether attached to
the adhesive pad substantially at the center, where the length of
the attachment can be equal to the width in the case of the T-pad
or some fraction or the width in the case of the center loaded pad.
In both cases the tether attached to the adhesive pad allows for
adjustment of the angle between the planar tether and the adhesive
pad from about 0.degree. to about 359.degree..
[0048] Elastic materials that may be used in the adhesive pads
include siloxane-based elastomers, urethane-based elastomers, and
acrylate-based elastomers. Polydimethylsiloxane (PDMS) belongs to a
group of polymeric organosilicon compounds that are commonly
referred to as silicones. PDMS, widely used silicon-based organic
polymer, has preferred rheological (or flow) properties. PDMS is
generally inert, non-toxic and non-flammable.
##STR00001##
A Polydimethylsiloxane
[0049] Other elastic materials that may be used in the adhesive
pads include polyurethanes, which are polymers of organic units
covalently joined by urethane (carbamate) links.
##STR00002##
A Polyurethane
[0050] A urethane linkage is produced by reacting an isocyanate
group, --N.dbd.C.dbd.O with a hydroxyl group, --OH. Polyurethanes
are produced by the polyaddition reaction of a polyisocyanate with
a polyalcohol (polyol) in the presence of a catalyst and other
additives. In this case, a polyisocyanate is a molecule with two or
more isocyanate functional groups,
R--(N.dbd.C.dbd.O).sub.n.gtoreq.2 and a polyol is a molecule with
two or more hydroxyl functional groups, R'--(OH).sub.n.gtoreq.2.
The reaction product is a polymer containing the urethane linkage,
--RNHCOOR'--. Examples of polyurethane monomers ("pre-polymers")
includes hydroxyl ended molecules, such as polyethylene glycol,
polypropylene glycol, poly tetramethylene glycol, or bisphenol A
(hydroxyl-containing monomers) and an aliphatic or aromatic based
isocyanate, such as methylene diphenyl diisocyanate, toluene
diphenyl diisocyanate, hexamethylene diisocyanate, isophorone
diisocyanate, or a polyisocyanate resulting from the combination of
multiple of these monomers (for example, three molecules of
methylene diphenyl diisocyanate form a trimer which contains three
isocyanate functional groups).
[0051] In one aspect, the invention generally relates to a
releasable, surface-adhesive device. The device includes an
adhesive pad and a tether component attached to the adhesive pad.
The adhesive pad includes: a planar backing layer having high
in-plane stiffness; and a planar layer of an elastic material
having an adhesive surface on at least one side for adhering to a
target surface, wherein the elastic material is impregnated onto
the backing layer on at least the side opposing the adhesive
surface. In certain preferred embodiment, the device further
comprises a holding component for load bearing. The holding
component being attachable to the tether component for connecting
an object to the device.
[0052] It is noted that the term "backing", as used herein,
includes but is not limited to the situation where the referred to
layer or material is the back (or the last) layer of the device
structure. According to this invention, a backing layer may be an
interior layer or component of a structural arrangement.
[0053] In certain embodiments, the adhesive pad includes: a planar
layer of an elastic material having an adhesive surface on one side
for adhering to a target surface; and a planar backing layer having
high in-plane stiffness, wherein the backing layer is impregnated
onto the layer of the elastic material on the side opposing the
adhesive surface.
[0054] In certain embodiments, the adhesive surface is
microscopically smooth. In certain embodiments, the adhesive
surface is microscopically patterned.
[0055] In certain embodiments, the backing layer is a fabric
backing layer.
[0056] In certain embodiments, the elastic material has a adhesive
surface area from about 0.01 cm.sup.2 to about 1,000 cm.sup.2
(e.g., about 0.01 cm.sup.2, 0.05 cm.sup.2, 0.1 cm.sup.2, 0.5
cm.sup.2, 1 cm.sup.2, 2 cm.sup.2, 5 cm.sup.2, 10 cm.sup.2, 20
cm.sup.2, 50 cm.sup.2, 100 cm.sup.2, 200 cm.sup.2, 500 cm.sup.2,
1,000 cm.sup.2) and a substantially uniform thickness from about
0.001 cm to about 0.1 cm. In certain embodiments, the planar layer
of the elastic material has a smooth adhesive surface area of
greater than about 0.01 cm.sup.2 and has a substantially uniform
thickness of less than about 0.001 cm. In certain embodiments, the
planar layer of the elastic material has a smooth adhesive surface
area of greater than about 0.05 cm.sup.2 and has a substantially
uniform thickness of less than about 0.005 cm. In certain
embodiments, the planar layer of the elastic material has a smooth
adhesive surface area of greater than about 0.1 cm.sup.2 and has a
substantially uniform thickness of less than about 0.01 cm. In
certain embodiments, the planar layer of the elastic material has a
smooth adhesive surface area of greater than about 0.2 cm.sup.2 and
has a substantially uniform thickness of less than about 0.5 cm. In
certain embodiments, the planar layer of the elastic material has a
smooth adhesive surface area of greater than about 0.5 cm.sup.2 and
has a substantially uniform thickness of less than about 0.2 cm. In
certain embodiments, the planar layer of the elastic material has a
smooth adhesive surface area of greater than about 1.0 cm.sup.2 and
has a substantially uniform thickness of less than about 0.1 cm. In
certain embodiments, the planar layer of the elastic material has a
smooth adhesive surface area of greater than about 5.0 cm.sup.2 and
has a substantially uniform thickness of less than about 0.05 cm.
In certain embodiments, the planar layer of the elastic material
has a smooth adhesive surface area of greater than about 10
cm.sup.2 and has a substantially uniform thickness of less than
about 0.02 cm. In certain embodiments, the planar layer of the
elastic material has a smooth adhesive surface area of greater than
about 100 cm.sup.2 and has a substantially uniform thickness of
less than about 0.01 cm. In certain embodiments, the planar layer
of the elastic material has a smooth adhesive surface area from
about 10 cm.sup.2 to about 100 cm.sup.2 and has a substantially
uniform thickness from about 0.01 cm to about 0.05 cm. In certain
embodiments, the planar layer of the elastic material has a smooth
adhesive surface area from about 1,000 cm.sup.2 to about 100
cm.sup.2 and has a substantially uniform thickness from about 0.5
cm to about 0.05 cm.
[0057] In certain embodiments, the elastic material has an
elasticity from about 0.05 MPa to about 50 MPa. In certain
embodiments, the elastic material has an elasticity from about 0.05
MPa to about 30 MPa. In certain embodiments, the elastic material
has an elasticity from about 0.05 MPa to about 10 MPa. In certain
embodiments, the elastic material has an elasticity from about 1
MPa to about 50 MPa. In certain embodiments, the elastic material
has an elasticity from about 1 MPa to about 30 MPa. In certain
embodiments, the elastic material has an elasticity from about 1
MPa to about 10 MPa.
[0058] In certain embodiments, the elastic material includes a
siloxane-based elastomer. In certain embodiments, the elastic
material includes a urethane-based elastomer. In certain
embodiments, the elastic material includes an acrylate-based
elastomers. In certain preferred embodiments, the elastic material
includes polydimethylsiloxane (PDMS). In certain embodiments, the
elastic material includes a polyurethane, for example, prepared
from polymerization of a hydroxyl ended polyethylene glycol with an
aliphatic or aromatic based polyisocyanate. Any suitable materials
may be used including styrene-butadiene-styrene elastomers and
other thermoreversible block copolymer elastomers; liquid
crystalline elastomers; natural rubber.
[0059] In certain embodiments, the material of the fabric backing
layer includes a natural fabric material or a synthetic fabric
material. In certain embodiments, the material of the fabric
backing layer includes a natural fabric material such as cotton,
hemp, wool, silk, bamboo string, cellulose, jute or pina. In
certain embodiments, the material of the fabric backing layer
includes a synthetic fabric of polyester, spandex, nylon, carbon
fiber, polyaramid, carbon fiber polyaramid hybrid, carbon fiber
basalt hybrid, fiberglass, or fiberglass hybrid. In certain
preferred embodiments, the material of the fabric backing layer
comprises a material selected from the group consisting of nylon,
carbon fiber, polyaramid, carbon fiber and polyaramid hybrid.
[0060] In certain embodiments, the device has an adhesive surface
area of 100 cm.sup.2 or greater and capable of bearing a weight or
at least 1200 N per 100 cm.sup.2 of adhesive surface area. In
certain embodiments, the device has an adhesive surface area of 100
cm.sup.2 or greater and capable of bearing a weight of at least
3150 N per 100 cm.sup.2 of adhesive surface area. In certain
embodiments, the device has an adhesive surface area of 1 cm.sup.2
or greater and capable of bearing a weight of at least 12.0 N per 1
cm.sup.2 of adhesive surface area. In certain embodiments, the
device has an adhesive surface area of 1 cm.sup.2 or greater and
capable of bearing a weight of at least 31.5 N per 1 cm.sup.2 of
adhesive surface area.
[0061] In certain embodiments, the tether is a fabric material, for
example, selected from synthetic fabrics like polyester, spandex,
nylon, carbon fiber, polyaramid, carbon fiber polyaramid hybrid,
carbon fiber basalt hybrid, fiberglass, carbon fiber, or fiberglass
hybrid, and natural fabrics including cotton, hemp, wool, silk,
bamboo string, cellulose, jute, and pina. In certain embodiments,
the tether is a non-fabric material, for example, selected from
leather, metal sheets, plastic sheets, or non-woven textiles. In
some embodiments, the material is made from chain-link meshes.
[0062] In another aspect, the invention generally relates to a
releasable, surface-adhesive device. The device includes: a planar
layer comprising an elastic material and having on one side an
adhesive surface for adhering to a target surface and on the other
side a backing layer having high in-plane stiffness, wherein the
elastic material impregnating into the backing layer; and a holding
component attachable to the backing layer for connecting an object
to the device. A portion of the backing layer extends beyond the
layer of the elastic material to form an area of the backing layer
un-impregnated with the elastic material, and the holding component
attaches to the backing layer at such area of the backing layer
un-impregnated with the elastic material.
[0063] In certain embodiment, the elastic material can extend
beyond the fabric layer on the "back side" of the pad. This design
may aid the establishment of uniform contact without sacrificing
the stiffness of the device that is directly related to the force
capacity of the adhesive device.
[0064] In yet another aspect, the invention generally relates to a
releasable, reusable surface-adhesive device. The device includes
an adhesive pad that has: a planar layer of an elastic material
having an adhesive surface on one side for adhering to a target
surface; and a planar backing layer having high in-plane stiffness,
wherein the backing layer is impregnated onto the layer of the
elastic material on the side opposing the smooth adhesive surface.
The device further includes a tether attached to the adhesive pad
substantially at the center of the adhesive pad and allowing
adjustment of the angle between the planar tether and the adhesive
pad from about 0.degree. to about 359.degree..
[0065] In certain embodiments, the adjustable angle between the
tether and the adhesive pad range from about 0.degree. to about
90.degree., for example, 15.degree., 30.degree., 45.degree., or
60.degree.. In certain other embodiments, the adjustable angle
between the tether and the adhesive pad range from about 90.degree.
to about 120.degree., for example, 95.degree., 110.degree.,
110.degree., or 115.degree.. In certain other embodiments, the
adjustable angle between the tether and the adhesive pad range from
about 120.degree. to about 360.degree., for example, 150.degree.,
180.degree., 210.degree., 270.degree. or 300.degree..
[0066] In yet another aspect, the invention generally relates to a
releasable, surface-adhesive device. The device includes an
adhesive pad, which has a planar layer of an elastic material
having a microscopically smooth or patterned adhesive surface on
one side for adhering to a target surface; and a planar fabric
backing layer having high in-plane stiffness, wherein the backing
layer is impregnated onto the layer of the elastic material on the
side opposing the adhesive surface. The device further includes a
tether component attached to the adhesive pad; and a holding
component for load bearing, the holding component being attachable
to the tether component for connecting an object to the device.
[0067] In yet another aspect, the invention generally relates to a
method for releasably holding a weight on a surface. The method
includes: (a) providing a releasable, surface-adhesive device
having an adhesive pad comprising a planar layer of an elastic
material having a microscopically smooth adhesive surface on one
side for adhering to a target surface; and a planar fabric backing
layer having high in-plane stiffness, wherein the fabric backing
layer is impregnated onto the layer of the elastic material on the
side opposing the smooth surface; a fabric tether attached to the
adhesive pad; and a holding component for load bearing attachable
to the fabric tether for connecting an object to the device; and
(b) attaching the weight to the holding component.
[0068] In yet another aspect, the invention relates to a method for
making a releasable, surface-adhesive device. The method includes:
(a) providing an elastic material; (b) providing a fabric backing
sheet; (c) curing the elastic material to impregnate the elastic
material into at least a portion of the fabric backing sheet to
form a pad having a layer of the elastic material with a smooth
adhesive surface; (d) attaching a weight-holding component to the
fabric backing sheet. The elastic material has an elasticity from
about 0.05 MPa to about 50 MPa, and the layer of the elastic
material has a thickness from about 0.0001 cm to about 0.1 cm.
[0069] In yet another aspect, the invention generally relates to a
method for making a releasable, surface-adhesive device. The method
includes: (a) providing a fabric backing sheet, on one side of
which is placed a substrate layer; (b) providing, on the other side
of the fabric backing sheet, a spacer-defined molding area; (c)
adding an elastic material into the spacer-defined molding area of
the fabric backing sheet; (d) covering the elastic material with a
top cover having a microscopically smooth or patterned surface; (e)
applying pressure against the top cover causing an intimate
interface between the top pad and the elastic material; (f) curing
the elastic material to impregnate the elastic material into at
least a portion of the fabric backing sheet to form a pad having a
layer of the elastic material with a microscopically smooth or
patterned adhesive surface; and (g) attaching a weight-holding
component to the fabric backing sheet. The elastic material has an
elasticity from about 0.05 MPa to about 50 MPa, and the layer of
the elastic material has a thickness from about 0.0001 cm to about
0.1 cm.
[0070] In certain embodiments, the ratio of storage to loss elastic
moduli is at least greater than about 10 (e.g., greater than 15,
20, or 50) at the operating temperature of interest.
[0071] The layer of the elastic material may have any size and
shape as a particular application requires, for example, it may
have a substantially circular outer boundary, a substantially
rectangular outer boundary, a substantially elliptical outer
boundary, or a substantially irregular outer boundary.
[0072] As stated herein, in some embodiments, the layer of an
elastic material includes two, three, four or more separate smaller
elastic material layer units or structures. The target surface may
be any suitable surfaces, including that of glass, metal, wood,
plastic, paper, cardboard, or concrete.
[0073] Repeated attachment and release of loads has been
demonstrated under pure shear and normal loading directions, as
well as controlled peel angles, with magnitudes of performance
unmatched by any existing products to our knowledge. For example,
an experimental device was able to support loads as great as 707
pounds with a 16 square inch T-pad (44 psi), with minimal force
required for detachment, a performance repeated on the same pad for
numerous cycles with negligible degradation in performance.
Additionally, an adhesive pad structure can be easily cleaned with
soap and water or a particle transfer material, such as a
viscoelastic, acrylic tape. The release mechanism may be designed
according to the principles disclosed herein to fit particular
applications.
[0074] The integrated adhesive pad approach of the invention
provides a robust platform for a wide-variety of applications. For
example, these structures can be used to support shelving for
books, displays, and electronic appliances (televisions, computers,
stereos, monitors, screens); hanging structures; auto trims; among
others. Furthermore, the current designs can be used to facilitate
climbing on vertical surfaces or overhangs that are made from a
variety of materials, such as glass, metal, wood, and drywall.
EXAMPLES
[0075] Force Vs. Displacement Tests
[0076] FIG. 5 shows exemplary force vs. displacement measurements
for characterizing maximum force supported under pure shear loading
for T-pad structures. (Fabric backing varied. All results were for
16 in.sup.2 pad with varying thicknesses labeled as `t` in the
legend.) The experiments were run on an Instron testing machine in
a single lab joint geometry where attachment was made between the
adhesive pad and a smooth clean glass substrate. The extension was
controlled to be 10 mm/min and the load was measured throughout the
test. The maximum load corresponds to the critical failure load,
which varies depending on fabric backing as shown.
[0077] FIG. 6 shows maximum shear force supported for various T-pad
configurations, natural data (which includes live geckos and
various attachment devices for geckos, beetles, spiders, crickets,
and flys), and non-fabric backed polymer coatings as a function of
the square root of interfacial area normalized by in-plane
compliance. Trend line follows predicted scaling relationship
demonstrating ability to predictably tune maximum shear force
performance.
Failure Force Tests
[0078] FIG. 7 shows failure force per unit width as a function of
peel angle for different T-pad configurations (total contact area
for each adhesive pad is 10.8 cm.sup.2, and the center loaded pad
connection is 2/3 the width). Demonstrating ability to tune
critical angle for easy release. Peel experiments were conducted on
an Instron 5500 R on clean glass at 10 mm/min, and the angle
between the applied load and substrate was varied between 0.degree.
and 90.degree..
[0079] FIG. 8 shows some simple examples of complete T-Pad
structure to support loads on various surfaces. The same nylon
fabric PDMS adhesive (A=16 in.sup.2 with thickness of 1 mm) pad
structure is used in all examples.
Fabrication of PDMS Adhesive Pads
[0080] FIG. 9 schematically illustrates an embodiment of
fabrication of PDMS adhesive pads. (A) To prepare PDMS adhesives,
molds were fabricated using glass slides. Uncured, degassed PDMS
oligomer and curing agent (Dow Corning Sylgard 184.TM.) 10:1 ratio
(w/w) were poured into the mold. The mold was constructed such that
its thickness was greater than the roughness of the fabric, which
allowed for a smooth surface finish on the adhesive after
fabrication. After the degassed PDMS was poured and allowed to
spread into the mold, a 6-8 minute pre-cure at 70.degree. C. was
performed before the application of the fabric to help support the
fabric during the subsequent cure. (B) Fabric was then placed over
the mold allowing the uncured PDMS to impregnate the fabric, and
was then cured at room temperature for 3 days. The fabric consisted
of a single piece that was cut so that the width overlaps the edges
of the mold to provide support, and the length was sufficiently
long to cover the mold and create the "tendon" structure. The
tendon can also be impregnated with elastomer to provide for equal
load sharing.
[0081] In another embodiment, the fabric was designed to be a
center loaded pad, such that a fabric tendon was stitched to the
center of the adhesive pad fabric. In this scheme, the tendon
structure was also impregnated with PDMS to ensure that the fabric
did not unravel during subsequent load application. This was
achieved by placing one separator sheet between the tendon and the
adhesive pad, then spreading PDMS across the tendon, followed by
placing a capping separator sheet on top of the impregnated tendon.
(C) After the PDMS was cured, the fabric adhesive was removed from
the mold and mechanically cut to size. A rigid mount ("skeleton")
consisting of 21/8'' thick plastic sheets were attached to the
bottom of the tendon using cyanoacrylate adhesive, which was then
allowed to cure for 6 hours.
[0082] FIG. 10 shows exemplary images of: (A) a photograph of a
nylon fabric PDMS adhesive, (B) a carbon fiber/Kevlar plain weave
fabric PDMS adhesive, and (C) an unidirectional carbon fiber
polyurethane adhesive. The center column shows a scanning electron
microscope (SEM) image of the side profile with the adhesive side
facing up, and the right column shows the smooth adhesive surface.
Scale bars in the optical photographs are 5 cm, and all scale bars
in the SEM images are 500 .mu.m.
Polyurethane Adhesives
[0083] Polyurethane adhesives have been synthesized by adding 1:1
ratio of functional groups of hydroxyl ended polyethylene glycol,
polypropylene glycol, and/or polytetramethylene glycol, with either
aliphatic or aromatic based polyisocyanates. Commercial kits of
polyurethanes have also been utilized in this application.
[0084] FIG. 11 shows modulus is plotted against frequency for an
example of polyurethane. The storage modulus is about an order of
magnitude greater than the loss modulus, showing that the sample
has predominantly solid-like, elastic properties. The modulus also
varies little over two orders of magnitude in frequency.
[0085] FIG. 12 schematically illustrates an embodiment of the
molding technique by which to form a pad with polyurethane. On top
of a polytetrafluoroethylene substrate fiber was placed for the
adhesive backing layer. A low-density polyethylene (LDPE) spacer
was placed on top of the fiber that allows for controlling
polyurethane (PU) thickness, and uncured PU prepolymer was poured
into the mold. A polydimethylsiloxane pad was then placed on top
with a glass plate, and finally the system was weighted with a 45
pound weight.
[0086] Utilizing this molding technique, a smooth adhesive surface
(utilizing a smooth PDMS top layer), or surface features (utilizing
a patterned PDMS top layer) can be achieved. The thickness of the
adhesive can be changed by modifying the thickness of the LDPE
spacer. This method may also be altered to work using a doctor
blade system, which would allow for mass production of adhesive
pads.
Loading Tests
[0087] Sample adhesive pads were tested using an Instron controlled
displacement test. Mechanical grips were attached to an Instron
5500 R, with a pane of glass attached to the grip on the crosshead,
and the adhesive pad secured to the bottom grip. The adhesive pad
was then adhered to the glass, and a displacement of 10 mm/min was
used until the adhesive detached from the glass. This test was
repeated multiple times to determine the average failure force, and
prove reusability. FIG. 13 shows that there is an initial loading
regime, and by finding the slope of this line one can find the
stiffness of the adhesive system that controls the total capacity
of the adhesive. The stiffness (and therefore, total capacity) for
these polyurethane adhesives is greater than previously recorded
values of stiffness. At the peak of this curve is the total
capacity (2950 N for this sample). After this peak the adhesive
releases from the glass, resulting in a drop in the registered
load. This test can be repeated, and we have shown good
reproducibility over 100 cycles of testing (FIG. 14).
[0088] Static load testing was also performed on these polyurethane
adhesives. A bar containing 136 kg of mass was connected via chain
to an adhesive pad, and was also supported by a pulley system.
Using the pulley system, the weights were raised until the adhesive
could be adhered to the glass adherend setup. The pulley system was
then lowered until the total load was supported by the adhesive.
Certain results of such tests are shown in FIG. 15, wherein the
tests were performed by holding 136 kg on glass surfaces.
[0089] As shown in FIG. 16, these polyurethane adhesives can be
used on a variety of substrates. These results were performed
similarly to previous loading tests, however, the glass pane was
either replaced with a new material, or a new material was adhered
to the surface of a glass pane. FIG. 17 shows the static load test
performed on (A) a 16 in.sup.2 center loaded PDMS adhesive pad
holding a 42'' flat panel television and (B) a center loaded
polyurethane adhesive pad holding a hooded sweatshirt on drywall.
FIG. 18 (A) shows schematic illustrations of the loading angle
dependence for the high capacity and easy release adhesive pads.
(B) Shows results of the angle dependence of the center loaded pad
compared to a single slab adhesive pad, where the center loaded pad
maintains a high failure force throughout various loading angles,
while still allowing for easy release.
INCORPORATION BY REFERENCE
[0090] References and citations to other documents, such as
patents, patent applications, patent publications, journals, books,
papers, web contents, have been made in this disclosure. All such
documents are hereby incorporated herein by reference in their
entirety for all purposes.
EQUIVALENTS
[0091] The representative examples are intended to help illustrate
the invention, and are not intended to, nor should they be
construed to, limit the scope of the invention. Indeed, various
modifications of the invention and many further embodiments
thereof, in addition to those shown and described herein, will
become apparent to those skilled in the art from the full contents
of this document, including the examples and the references to the
scientific and patent literature included herein. The examples
contain important additional information, exemplification and
guidance that can be adapted to the practice of this invention in
its various embodiments and equivalents thereof.
* * * * *